Quartz crystal oscillator has been used for several decades and played an important role in the electronics industry for its high frequency stability. Especially under a high development of the information technology industry, this quartz crystal oscillator is full of vitality much more. The quartz crystal oscillators served as a standard frequency source or a pulse signal source provide a frequency reference in telecommunications, satellite communications, Mobile Phone System, Global Positioning System, navigation, remote control, aerospace, high-speed computer, precise measuring instrument and consumable electronic products, which can not be replaced by other oscillators. The quartz crystal oscillators generally include non-temperature compensated crystal oscillator, temperature compensated crystal oscillator, voltage-controlled crystal oscillator, oven controlled crystal oscillator, and digital/μp compensated crystal oscillator. Therein the oven controlled crystal oscillator has the highest frequency stability and the highest precision, and the performances of aging rate, temperature stability, long-term stability, and short-term stability are excellent, therefore the oven controlled crystal oscillator is widely used in electronic equipments such as Global Positioning System, communications, measurement, telemetry and remote, spectrum and network analyzer.
As the oscillation characteristic of the quartz crystal varies with the temperature, thus the output frequency of the quartz crystal oscillator is affected. The oven controlled crystal oscillator is such a crystal oscillator that aims at reducing the output frequency variation of the oscillator caused by the change of external temperature to the minimum, by utilizing a thermostatic bath to keep a constant temperature of the crystal oscillator or quartz crystal. In the prior art, for further reducing the impact resulted by the temperature variation and improving the frequency stability of the oven controlled quartz oscillator, the oven controlled crystal oscillator generally includes an outer circuit board and an inner circuit board having a crystal oscillation circuit. As the working performance of the crystal oscillation circuit is easy to be affected by the temperature, thus the inner circuit board is positioned in the thermostatic bath. The outer circuit board including a temperature control circuit and a power supply circuit is fixed beneath the thermostatic bath, and electrically connected with the inner circuit board. Although the thermostatic bath can ensure the frequency stability of the oven controlled crystal oscillator, the oven controlled crystal oscillator of the prior art has the following problems. Firstly, the thermostatic bath is located over the outer circuit board, thereby increasing the height of the oven controlled crystal oscillator, which goes against a compact design. Secondly, the inner circuit board applies a way that configures a pin extending from the bottom of the inner circuit board, so that the inner circuit board is electrically connected with the outer circuit board located at the lower portion of the thermostatic bath. With this structure, the performance of the electric connection between the inner circuit board and the outer circuit board may be affected due to the vibration occurred during the assembling process, or the thermostatic bath may disengage from the outer circuit board due to the vibration.
Thus, there is a need for an improved oven control crystal oscillator with a high stability and a thin structure to overcome the above drawbacks.